Relationships of Genetic Background Among Pyricularia Species, the Blast Pathogens on Gramineous Plants

利用日本山区收集的Panicum miliaceum （Pm）和Setaria itarica （Si）的种子和真菌菌株，研究了两者致病性分化的关系。寄主范围：利用7个禾本科植物族进行接种试验。1) pm菌株侵染了27种植物中的18种。对水稻、稻瘟病菌和coracana Eleusine （Ec）均无致病性。2) si菌株侵染31种中的14种。日本和中国产的日本芥有小种，对水稻、Pm和ec2均无致病性。配种方式：将Ec配种类型A和A的标准分离株与Pm和si分离株进行杂交，确定配种方式。1) 39株pm菌株分为a型（26株），无a型；2) si株为6株a型，9株a型。交配能力：1)pm -菌株与ec -菌株进行了交配，但子囊孢子不完整。pm -品系与水稻品系和si -品系均未交配。2)硅系与水稻品系和小麦品系均可交配，部分子囊孢子可育。si -品系与ec -品系杂交的滞后染色体比例为27% ~ 46%，si -品系与小麦品系杂交的滞后染色体比例为24% ~ 35%。基于这些结果，来自Pm和Si的稻瘟病菌已经分化为两个品系（特殊形式），尽管这两种植物都是在同一地区种植的。

Seeds and Pyricularia strains from Panicum miliaceum (Pm) and Setaria itarica (Si) collected from a mountainous area of Japan were used in order to examine the relationships of differentiation of pathogenicity.l. Host range : Seven tribes of gramineous plants were utilized for inoculation tests. 1) Pm-strain attacked eighteen species among twenty seven. No pathogenicity was found against rice, Si and Eleusine coracana (Ec). No differentiated races were detected to Panicum miliaceum from Japan. 2) Si-strain attacked fourteen species among thirty one. There were races to Setaria itarica from Japan and China and no pathogenicity against rice, Pm and Ec.2. Mating type : Standard isolates of mating types A and a of Ec were crossed with isolates of Pm and Si-strains to decide the mating type. 1) Pm-strain was classified into a-type (26 isoiates out of 39 isolates) and no A-type. 2) Si-strain was six A-type and nine a-type.3. Mating ability : 1) Pm-strain was mated with Ec-strain, but ascospores were incomplete. Pm-strain was not mated with either rice-strain or Si-strain. 2) Si-strain was mated with both rice -strain and wheat-strain and some ascospores were fertile. Laggingchromosomes appeared 27 to 46% in the cross between Si-strain and Ec-strain and 24 to 35% in the cross between Si-strain and wheat-strain.Based on these results, Pyricularia from Pm and Si has differentiated into two strains (forma specialis), though both plants have been raised in the same area.